This paper presents the results of a discourse analysis of documents describing six different eco-city projects: Dongtan Eco-City, Masdar City, Sonoma Mountain Village, Hammarby Sjöstad, Eco-village Ithaca, and Malmö bo01. The aim of the research was to uncover the diversity underneath the various uses of the term eco-city, and to determine the extent of convergence or divergence in the way projects conceive of what an eco-city should be. The research looked at five categories of urban sustainability discourse: the aspect of sustainability emphasised, whether eco-city projects saw themselves as a model for future urban development or as an educational tool, the way in which eco-cities proposed to make urban living more sustainable, the extent to which projects looked at achieving sustainability by design or through governance and management, and the type of actors that play a role in the eco-city. The results suggest that there is a great deal of diversity among projects considered to be eco-cities. In this sense, we argue, it is better to think of the eco-city as an ambition or objective which there will be multiple ways to achieve.